i8254: use QEMU_ALIGN_DOWN

I used the clang-tidy qemu-round check to generate the fix:
https://github.com/elmarco/clang-tools-extra

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>

hw/timer/i8254_common.c

@@ -93,15 +93,15 @@ int64_t pit_get_next_transition_time(PITChannelState *s, int64_t current_time)
         }
         break;
     case 2:
-        base = (d / s->count) * s->count;
+        base = QEMU_ALIGN_DOWN(d, s->count);
         if ((d - base) == 0 && d != 0) {
             next_time = base + s->count;
         } else {
             next_time = base + s->count + 1;
         }
         break;
     case 3:
-        base = (d / s->count) * s->count;
+        base = QEMU_ALIGN_DOWN(d, s->count);
         period2 = ((s->count + 1) >> 1);
         if ((d - base) < period2) {
             next_time = base + period2;